Thermal seal between manifold and nozzle

ABSTRACT

A seal is provided between a nozzle and a manifold. The seal provides a melt channel between an outlet of the manifold and a nozzle channel. The seal has higher thermal expansion coefficient than both the nozzle and the manifold to provide an improved seal between the manifold and the nozzle when the injection molding apparatus is at an operating temperature.

FIELD OF THE INVENTION

[0001] The present invention relates generally to an injection molding apparatus and, in particular, to an improved seal between a manifold and a nozzle.

BACKGROUND OF THE INVENTION

[0002] A common problem associated with hot runner injection molding systems is the leaking of molten plastic that can occur between the manifold and the nozzle. Leaking is typically caused by operation of the hot runner injection molding system outside of the designated operating window. There are many different nozzle designs of the prior art that attempt to stop leakage from occurring.

[0003] A pair of spacers located between a manifold and a cover plate or a hot runner plate, such as disclosed in U.S. Pat. Nos. 6,309,207, 6,062,846 and U.S. patent application Ser. No. 2001/0011415, apply a contact pressure between the nozzle body melt channel and the manifold melt channel to achieve a seal therebetween. The spacers are arranged in series with a first spacer abutting the manifold and a second spacer abutting the cover plate. The second spacer has a different response characteristic to compressive pressures than the first spacer.

[0004] WO 01/87570 A1 discloses a non-flat sealing interface, which is provided between a nozzle and a manifold. A spring urges the nozzle against the manifold to produce a pressure distribution with a peak sealing pressure that occurs adjacent the nozzle and manifold melt channels. Similarly U.S. Pat. No. 5,896,640 discloses a sealing insert that abuts a nozzle shoulder. The sealing insert generates an angular sealing force and maintains sealing contact between the nozzle and manifold channels. The sealing insert produces a peak sealing pressure that occurs adjacent the nozzle and manifold channels.

[0005] It is an object of the present invention to provide a novel thermal seal for reducing the leakage between a manifold and a nozzle.

SUMMARY OF THE INVENTION

[0006] According to one aspect of the present invention there is provided an injection molding apparatus comprising:

[0007] a manifold having a manifold channel, the manifold channel having an inlet for receiving a melt stream of moldable material and an outlet for delivering the melt stream to a nozzle channel of a nozzle;

[0008] a sealing element provided between the nozzle and the manifold, the sealing element including a melt channel for receiving the melt stream from the outlet of the manifold channel and delivering the melt stream to the nozzle channel; and

[0009] a mold cavity for receiving the melt stream from the nozzle channel, the nozzle channel communicating with the mold cavity through a mold gate;

[0010] wherein the sealing element has a higher thermal expansion coefficient than both the nozzle and the manifold.

[0011] According to another aspect of the present invention there is provided an injection molding apparatus comprising:

[0012] a manifold having a manifold channel for receiving a melt stream of moldable material under pressure;

[0013] a manifold plug provided in the manifold, the manifold plug having a manifold plug channel formed therein, the manifold plug channel having an inlet for receiving the melt stream from the manifold channel and an outlet for delivering the melt stream to a nozzle channel of a nozzle; and

[0014] a mold cavity for receiving the melt stream from the nozzle channel, the nozzle channel communicating with the mold cavity through a mold gate;

[0015] wherein the manifold plug has a higher thermal expansion coefficient than both the nozzle and the manifold.

[0016] According to yet another embodiment of the present invention there is provided an injection molding apparatus comprising:

[0017] a manifold having a manifold channel, the manifold channel having an inlet for receiving a melt stream of moldable material under pressure and an outlet;

[0018] a nozzle having nozzle body and a nozzle head, the nozzle head being located adjacent an outlet surface of the manifold, the nozzle having a nozzle channel for receiving the melt stream from the outlet of the manifold channel; and

[0019] a mold cavity for receiving the melt stream from the nozzle channel, the nozzle channel communicating with the mold cavity through a mold gate;

[0020] wherein at least a portion of the nozzle head has a higher thermal expansion coefficient than both the nozzle body and the manifold.

[0021] The present invention provides advantages in that the sealing element provides a continuous sealed melt channel between the manifold and the nozzle to minimize leakage at the connection therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the present invention will now be described more fully with reference to the accompanying drawings in which:

[0023]FIG. 1 is a side sectional view of a first embodiment of an injection molding apparatus of the present invention;

[0024]FIG. 2 is a side sectional view of parts of an injection molding apparatus of a further embodiment of the present invention;

[0025]FIG. 3 is a side sectional view of the injection molding apparatus of FIG. 2 in an operating condition;

[0026]FIG. 4 is a side sectional view of parts of a further embodiment of an injection molding apparatus of the present invention;

[0027]FIG. 5 is a side sectional view of the injection molding apparatus of FIG. 4 in an operating condition;

[0028]FIG. 6 is a side sectional view of parts of yet a further embodiment of an injection molding apparatus of the present invention;

[0029]FIG. 7 is a side sectional view of the injection molding apparatus of FIG. 6 in an operating condition;

[0030]FIG. 8 is a side sectional view of a further embodiment of an injection molding apparatus of the present invention;

[0031]FIG. 9 is a side sectional view of the injection molding apparatus of FIG. 8 in the operating condition;

[0032]FIG. 10 is a side sectional view of a further embodiment of an injection molding apparatus of the present invention;

[0033]FIG. 11 is a side sectional view of a further embodiment of an injection molding apparatus of the present invention;

[0034]FIG. 12 is a side sectional view of still a further embodiment of an injection molding apparatus of the present invention;

[0035]FIG. 13 is a side sectional view of a further embodiment of an injection molding apparatus;

[0036]FIG. 14 is a side sectional view of a further embodiment of an injection molding apparatus;

[0037]FIG. 15 is a side view of a sealing insert of the injection molding apparatus of FIG. 14; and

[0038]FIG. 16 is a cross-sectional view taken along on line A of FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] Referring now to FIG. 1, an injection molding apparatus is generally indicated by reference numeral 10. The injection molding apparatus comprises a manifold 12 having a manifold channel 14 extending therethrough. A manifold bushing 16 that is located at an inlet of the manifold channel 14 receives a melt stream of moldable material from a machine nozzle (not shown). The melt stream flows through the manifold channel 14 and is delivered to outlets 18, as indicated by the arrows 17. Manifold heaters 15 are provided in the manifold 12 to maintain the melt stream at a desired temperature.

[0040] Nozzles 20 are located between the manifold 12 and respective mold cavities 30, which are formed in mold cavity plates 35. Each nozzle 20 includes a nozzle channel 22 for receiving the melt stream from the respective manifold outlet 18 and delivering the melt stream to the respective mold cavity 30. Mold gates 31 are provided at the entrance to the mold cavities 30, adjacent tips 24 of the nozzles 20. Each nozzle 20 includes a valve pin 21 that is driven by a valve piston 23. The valve pins 21 are selectively movable to open and close the respective mold gates 31. Each nozzle 20 is further provided a heater 40, which helps to maintain the melt stream at a desired temperature as it passes through the nozzle 20. Cooling channels 33 are located adjacent the mold cavities 30 in order to aid in the cooling thereof.

[0041] The injection molding apparatus 10 of FIG. 1 further includes a sealing element or a sealing insert 44 that is located between the nozzle 20 and the manifold 12. The sealing insert will be described in more detail in relation to FIGS. 2 to 7. In each of the following injection molding apparatus embodiments, like reference numerals represent like parts.

[0042] Referring to FIG. 2, another embodiment of an injection molding apparatus 10 a is shown. In this embodiment, a manifold plate 36 abuts the mold cavity plate 35 a

[0043] A nozzle shoulder 32 is provided at an upper end of the nozzle 20 a. The nozzle shoulder 32 includes an upper surface 26, which abuts an outlet surface 28 of a manifold 12 a. The nozzle shoulder 32 includes a downwardly directed spacing flange 34 that is supported by the manifold plate 36.

[0044] A backing plate 50 is located adjacent the manifold 12 a and is offset by a gap 51. A spring 52 is provided between the backing plate 50 and the manifold 12 a. The spring 52 may alternatively be a rigid spacer. The spring 52 absorbs movement of the manifold 12 a caused as a result of thermal expansion, which occurs when the manifold 12 a and nozzle 20 a heat up to the operating temperature range.

[0045] The nozzle 20 a further includes a recess 41 that is formed in an upper surface 26, or manifold contacting surface, of the nozzle 20 a. The depth of the recess 41 is delimited by a shoulder 46. A sealing insert 44 a, which is generally a sleeve having a bore 47, is nested in the recess 41. The melt stream flows through the bore 47 from a manifold outlet 18 a and into nozzle channel 22 a. The sealing insert 44 a has a length 60 and a wall thickness 62. The wall thickness 62 is typically in the range of 2 to 3 mm. The sealing insert 44 a and manifold 12 a are arranged so that a cold clearance, indicated at 48, is provided between the sealing insert 44 a and the manifold 12 a.

[0046] The sealing insert 44 a has a higher thermal conductivity than both the manifold 12 a and the nozzle 20 a, which are typically comprised of tool steels such as H13 or P20 steel, for example. The sealing insert 44 a may be comprised of copper, beryllium copper, brass, carbide or some steels. Alternatively, any suitable material having a higher thermal conductivity than the manifold 12 a and nozzle 20 a may be used.

[0047]FIG. 2 shows the injection molding apparatus 10 a in a cold, or non-operating, condition, in which the apparatus 10 a is below an operating temperature. This condition occurs prior to operation of the injection molding apparatus 10 a. Referring to FIG. 3, the injection molding apparatus 10 a is shown in the operating condition, in which the temperature of the injection molding apparatus 10 a is in an operating temperature range. As shown, the sealing insert 44 a has lengthened to remove the cold clearance 48 and impart a sealing force, as indicated by arrows 54, on the outlet surface 28 of the manifold 12 a.

[0048] In operation, the injection molding apparatus 10 a starts in the cold condition of FIG. 2, in which all of the components are at generally the same ambient temperature. During operation, the manifold 12 a having a manifold channel 14 a and the nozzle 20 a having nozzle channel 22 a are heated and then maintained at their respective temperatures so that the melt stream may flow unhindered into the melt cavity 30 a, which is chilled. The nozzle 20 a and manifold 12 a must maintain tight alignment with each other while in the operating temperature range. The manifold 12 a and the nozzle 20 a may be subject to different amounts of heat expansion, particularly if they are comprised of different materials. In the injection molding apparatus of FIG. 2, the manifold 12 a is allowed to have a lateral displacement relative to the nozzle 20 a because the nozzle 20 a is not coupled to the manifold 12 a by a fastener.

[0049] As the manifold 12 a heats up to operating temperature, the nozzle 20 a is heated by contact with the manifold 12 a and also by heater 40. Due to heat expansion, the manifold 12 a applies pressure to nozzle 20 a and the spring 52. At the same time, due to the heat expansion of the nozzle 20 a, the nozzle 20 a applies pressure to the outlet surface 28 of the manifold 12 a. As a result, the spring 52 compresses to avoid damage to the manifold 12 a and nozzle 20 a. The sealing insert 44 a also responds to the temperature increase by expanding more than the nozzle 20 a and thus applying sealing force to the outlet surface 28 of the manifold 12 a. Because the sealing insert 44 a has a high thermal conductivity, the length 60 of the sealing insert 44 a increases by a larger amount than the surrounding components. This is shown by length 60′ in FIG. 3. The pressure applied to the manifold 12 a by the sealing insert 44 a is greater than the injection forces generated by the melt stream, which attempt to push the manifold 12 a and nozzle 20 a apart and create a clearance for the melt stream to leak under pressure.

[0050] The spring 52 is relatively stiff and compresses to reduce forces that may be large enough to damage the nozzle 20 a or the manifold 12 a. The spring 52 does not compress due to the sealing force applied by the sealing insert 44 a. Instead, the sealing insert 44 a is designed to at least partially collapse if the sealing force applied is too large. The sealing insert 44 a is a relatively inexpensive component and therefore, is easily replaced if damaged.

[0051] It will be appreciated by a person skilled in the art that the length 60 and wall thickness 62 of the sealing insert 44 a may be varied to suit the sealing requirements of a particular application.

[0052] Turning now to FIG. 4, another embodiment of an injection molding apparatus 10 b is shown. The injection molding apparatus 10 b is similar to the injection molding apparatus 10 and 10 a of FIG. 1 and FIGS. 2 and 3, respectively. A nozzle 20 b includes a shoulder flange 70 that extends outwardly from a top portion thereof. The shoulder flange 70 is coupled to a manifold 12 b by a fastener 72. Additional fasteners 72 may be used, however, for simplicity only one is shown in the Figures.

[0053] A manifold plate 36 b abuts a mold cavity plate 35 b of mold cavity 30 b and supports the nozzle 20 b. The nozzle 20 b engages mounting elements 38, which extend from the inner wall 42 of the manifold plate 36 b, to locate the nozzle 20 b and manifold 12 b, which is fastened thereto, relative to the mold cavity plate 35 b.

[0054] A first recess 41 b having a shoulder 46 b is formed in the upper surface 26 b of the nozzle 20 b. A second recess 74 having a shoulder 76 is formed in an outlet surface 28 b of the manifold 12 b. A sealing insert 44 b having a bore 47 b is nested in the recess 41 b and extends beyond an upper surface 26 b of the nozzle 20 b through a portion of second recess 74. The melt stream flows through bore 47 b of the sealing insert 44 b from a manifold outlet 18 b to a nozzle channel 22 b.

[0055] The sealing insert 44 b has a length 60 b and is generally similar in construction to the sealing insert 44 a of FIGS. 2 and 3. The sealing insert 44 b and manifold 12 b are arranged so that a cold clearance, indicated at 48 b, is provided between the sealing insert 44 b and the shoulder 76 of the manifold 12 b.

[0056] In operation, the injection molding apparatus 10 b starts in the cold condition of FIG. 4 and is heated to the operating condition of FIG. 5, as has been described in relation to FIGS. 2 and 3. As the manifold 12 b having a manifold channel 14 b heats up to operating temperature, the nozzle 20 b having a nozzle channel 22 b is heated by contact with the manifold 12 b and also by heaters 40. The fastener 72 typically expands along with the manifold 12 b and nozzle 20 b. The expansion of the manifold 12 b and nozzle 20 b assembly is absorbed by spring 52. Gap 51 is reduced so that damage to the manifold 12 b and nozzle 20 b is avoided.

[0057] At the same time, the sealing insert 44 b expands and applies a sealing force, in the direction indicated by arrow 54 b, to the manifold shoulder 76, as is shown in FIG. 5. Because the sealing insert 44 b has a higher thermal conductivity than both the nozzle 20 b and manifold 12 b, the length 60 b of the sealing insert 44 b increases by a larger amount than the surrounding components. This is shown by length 60 b′ in FIG. 5. The pressure applied to the manifold shoulder 76 by the sealing insert 44 b is greater than the injection forces of the melt stream, which attempt to push the manifold 12 b and nozzle 20 b apart.

[0058] The sealing insert 44 b of the injection molding apparatus 10 b additionally allows for location of the nozzle 20 b relative to the manifold 12 b. The sealing insert 44 b projects beyond the upper surface 26 b of the nozzle 20 b so that the nozzle channel 20 b can be aligned with the manifold outlet 18 b.

[0059] Turning now to FIGS. 6 and 7, another embodiment of an injection molding apparatus 10 c is shown. The injection molding apparatus 10 c is similar to the injection molding apparatus 10 b of FIGS. 4 and 5, however, the injection molding apparatus 10 c incorporates a sealing insert 44 c similar to sealing insert 44 a of FIGS. 2 and 3. A manifold 12 c having a manifold channel 14 c is similar to the manifold 12 b of FIGS. 4 and 5, however, it has a flat outlet surface 28 c and does not incorporate the second recess 74. Operation of the embodiment of FIGS. 6 and 7 need not be described in detail as the sealing action of the sealing insert 44 c to reduce leakage between nozzle 20 c and manifold 12 c has generally been described in relation to FIGS. 1-5.

[0060] Referring to FIG. 8, a further embodiment of an injection molding apparatus 10 d is shown in a cold, or non-operating condition. A manifold 12 d includes a manifold channel 14 d for delivering a melt stream through an outlet 18 d to a nozzle channel 22 d of a nozzle 20 d. A collar 90 is provided between an upper surface 26 d of the nozzle and an outlet surface 28 d of the manifold 12 d. The collar 90 includes a shoulder portion 32 d and a spacing flange portion 34 d.

[0061] A manifold plug 80 fits into a bore 82 in the manifold 12 d and forms part of the channel 14 d. The manifold plug 80 is press fit into the bore 82 in a manner that would be apparent to one of ordinary skill in the art. A cold clearance gap 84 is exists between a lower surface 86 of the manifold plug 80 and the outlet surface 28 d of the manifold 12 d. The manifold plug 80 behaves in a similar manner as the sealing insert 44 that has been previously described in relation to FIGS. 1-7. In addition, the manifold plug 80 is formed of similar materials.

[0062] As the manifold 12 d heats up to operating temperature, the manifold plug 80 lengthens to eliminate the cold clearance gap 84, as shown in FIG. 4, and apply pressure to the nozzle 20 d, via collar 90. The operating condition, in which leakage between the manifold 12 d and the collar 90 is reduced due to the manifold plug 80, is shown in FIG. 9.

[0063]FIG. 10 shows a further embodiment of an injection molding apparatus 10 f. The injection molding apparatus 10 f is a multi-cavity injection molding apparatus having a plurality of nozzles 20 f, which inject melt into a plurality of mold cavities 30 f. FIG. 10 shows a single nozzle 20 f and mold cavity 30 f for simplicity. The injection molding apparatus 10 f comprises a manifold 12 f having a manifold channel 14 f extending therethrough for receiving a melt stream of moldable material from a machine nozzle (not shown). The melt stream flows through the manifold channel 14 f and is delivered to an outlet 18 f of the manifold 12 f. Manifold heaters 15 f are provided in the manifold 12 f to maintain the melt stream at a desired temperature.

[0064] A backing plate 50 f is located adjacent the manifold 12 f and is offset by a gap 51 f. A spring 52 f is provided between the backing plate 50 f and the manifold 12 f.

[0065] Nozzle 20 f is located between the manifold 12 f and the mold cavity 30 f, which is formed in a mold cavity plate 35 f. Each nozzle 20 f includes a nozzle channel 22 f for receiving the melt stream from the manifold outlet 18 f and delivering the melt stream to the mold cavity 30 f. A mold gate 31 f is provided at the entrance to the mold cavity 30 f, adjacent a tip 24 f of the nozzle 20 f. Each nozzle 20 f is provided with one or more heaters 40 f that help to maintain the melt stream at a desired temperature as it passes through the nozzle 20 f.

[0066] A nozzle shoulder 32 f is provided at an upper end of the nozzle 20 f. The nozzle shoulder 32 f includes an upper surface 26 f, which abuts an outlet surface 28 f of the manifold 12 f. A spacer 34 f is located between a lower surface of the nozzle shoulder 32 f and a contact surface 37 of the manifold plate 36 f. The spacer 34 f is made of a low thermally conductive material such as titanium or ceramic, for example. As would be apparent to one of ordinary skill in the art, spacer 34 f positions and aligns nozzle 20 f with respect to manifold 12 f and mold cavity 30 f.

[0067] A manifold plate 36 f abuts the mold cavity plate 35 f. Cooling channels 33 f extend through the manifold plate 36 f adjacent the mold cavity 30 f in order to aid in the cooling of melt therein.

[0068] The nozzle 20 f includes a recess 41 f that is formed in the upper surface 26 f, or manifold contacting surface, of the nozzle 20 f. The recess 41 f is delimited by a shoulder 46 f. A sealing insert 44 f having a bore 47 f is nested in the recess 41 f. When the injection molding apparatus 10 f is in the cold condition a clearance (not shown) is provided between the sealing insert 44 f and the outlet surface 28 f of the manifold 12 f. The wall thickness of the sealing insert 44 f is typically in the range of 2 to 3 mm.

[0069] The sealing insert 44 f has a higher thermal conductivity than both the manifold 12 f and the nozzle 20 f, which are typically comprised of tool steels such as H13 or P20 steel, for example. The sealing insert 44 f may be comprised of copper, beryllium copper, brass, carbide or some steels. Alternatively, any suitable material having a higher thermal conductivity than the manifold 12 f and nozzle 20 f may be used.

[0070] In operation, the injection molding apparatus 10 f starts in the cold condition, in which all of the components are at generally the same ambient temperature. During operation, the manifold 12 f and the nozzle 20 f are heated and then maintained at their respective temperatures so that the melt stream may flow unhindered into the melt cavity 30 f, which is chilled. As the injection molding apparatus 10 f heats up to operating temperature (shown in FIG. 10) the sealing insert 44 f expands. Because the sealing insert 44 f has a higher thermal expansion coefficient, the length of the sealing insert 44 f increases by a larger amount than the surrounding components, including the nozzle 20 f and the manifold 12 f. As such, the sealing insert 44 f applies a sealing force to the outlet surface 28 f of the manifold 12 f. The expansion of the sealing insert 44 f may, in fact, cause the upper surface 26 f of the nozzle 20 f and the outlet surface 28 f of the manifold 12 f to move apart slightly, however, fluid communication between the components is sealed. The bore 47 f of the sealing insert 44 f provides a continuous, sealed path for melt to flow between the manifold outlet 18 f and the nozzle channel 22 f.

[0071] A further embodiment of an injection molding apparatus is generally shown at 10 g of FIG. 11 in which a nozzle 20 g having a nozzle body 104 and a nozzle head, or shoulder, 102 is shown. The nozzle head 102 operates similarly to the sealing insert 44 of the previous embodiments by expanding more than the surrounding components to produce a seal between manifold channel 14 g of manifold 12 g and nozzle channel 22 g. The nozzle body 104 and nozzle head 102 are coupled together by brazing or a threaded connection, for example (not shown). In this embodiment, the head 102 can be made of different materials than the body 104. The head 102 is made of a material having higher thermal conductivity and is heated by manifold 12 g. Spacer 34 g is a separate part that is made of a material having low thermal conductivity. As would be apparent to one of ordinary skill in the art, spacer 34 g positions and aligns nozzle 20 g with respect to manifold 12 g and mold cavity 30 g.

[0072]FIG. 12 shows yet a further embodiment of an injection molding apparatus 10 h. In this embodiment a nozzle head 102 h includes a sleeve portion 106 that is nested in a recess 41 h provided in a nozzle body 104 h. The nozzle head 102 h is made of a material having higher thermal conductivity than nozzle body 104 h and is heated by manifold 12 h. The injection molding apparatus 10 h is shown in an operating condition and the nozzle head 102 h exerts a sealing force 54 h in a similar manner as the sealing inserts 44 of the previous embodiments.

[0073] Referring to FIG. 13, a further embodiment of an injection molding apparatus 10 i is shown. A sealing insert 44 i is mounted in a recess 41 i that is formed in an outlet surface 28 i of the manifold 12 i. The recess 41 i surrounds an outlet 18 i of manifold channel 14 i. The sealing insert 44 i includes a bore 47 i that is aligned with the manifold channel 14 i to provide a continuous path between manifold channel 14 i and nozzle channel 22 i.

[0074] A spacer 100 separates the backing plate 50 i and the manifold 12 i. The spacer 100 is typically comprised of a thermal insulating material such as titanium or ceramic, for example. The spacer 100 performs a similar function as spring 52 of FIG. 2, however, because it is comprised of a thermal insulating material, the size of the gap between the manifold 12 i and the backing plate 50 i remains generally constant.

[0075] The injection molding apparatus 10 i of FIG. 13 is shown in the operating condition. In this condition, the sealing insert 44 i is in an expanded state in which the length 60 i of the sealing insert 44 i fills recess 41 i and the sealing insert 44 i exerts a sealing force on nozzle head 102 i of nozzle 20 i. The sealing insert 44 i functions in a similar manner as the manifold plug 80 of FIGS. 8 and 9, which has been previously described.

[0076] A further embodiment of an injection molding apparatus 10 j is shown in FIG. 14. In this embodiment, a manifold 12 j having a manifold channel 14 j extending therethrough receives a melt stream of moldable material from a machine nozzle (not shown). Nozzles 20 j are provided adjacent the manifold 12 j. Each nozzle 20 j includes a nozzle channel 22 j for receiving the melt stream from a respective manifold outlet 18 j and delivering the melt stream through a nozzle tip (not shown) to a respective mold cavity (not shown). Each nozzle 20 j is further provided with a heater 40 j that is coupled to a connector 43. The heater 40 j helps to maintain the melt stream at a desired temperature as it passes through the nozzle 20 j.

[0077] The manifold 12 j includes a recess 41 j that is formed in the outlet surface 28 j of the manifold 12 j. The recess 41 j is stepped and includes a first threaded portion 110 and a first generally smooth portion 112. The recess 41 j is sized to receive a sealing insert 44 j. The sealing insert 44 j, which is shown in FIGS. 15 and 16, includes a first end surface 114, a second end surface 116 and a bore 47 j that extends therethrough. An outer surface 118 of the sealing insert 44 j includes a neck 120 that is provided between a second threaded portion 122 and a second generally smooth portion 124. The second threaded portion 122 of the sealing insert 44 j is sized to mate with the first threaded portion 110 of the recess 41 j to secure the sealing insert 44 j to the manifold 12 j. As shown, the sealing insert 44 j further includes a pair of tooling apertures 126 (only one tooling aperture shown in FIG. 15) that are formed in the second end surface 116 thereof to allow for installation.

[0078] The sealing insert 44 j and manifold 12 j are arranged so that a cold clearance is provided between the sealing insert 44 j and a mating surface 26 j of the nozzle 20 j. The sealing insert 44 j is comprised of a material having a higher thermal conductivity than both the manifold 12 j and the nozzle 20 j. The sealing insert 44 j may be comprised of copper, beryllium copper, brass, carbide or some steels. Any suitable material having a higher thermal conductivity than the manifold 12 j and nozzle 20 j may be used. The wall thickness of the sealing insert 44 j is typically in the range of 2 to 4 mm.

[0079] In operation, the injection molding apparatus 10 j starts in a cold condition, in which all of the components are at generally the same ambient temperature. During operation, the manifold 12 j and the nozzle 20 j are heated and then maintained at their respective temperatures so that the melt stream may flow unhindered into the melt cavity. The heated, or operating, condition is shown in FIG. 14. The sealing insert 44 j responds to the temperature increase by expanding more than the manifold 12 j and thus applying sealing force to the mating surface 26 j of the nozzle 20 j. Because the sealing insert 44 j has a high thermal conductivity, the length 60 j of the sealing insert 44 j increases by a larger amount than the surrounding components. The pressure applied to the nozzle 20 j by the sealing insert 44 j is greater than the injection forces generated by the melt stream, which attempt to push the sealing insert 44 j and the nozzle 20 j apart and create a clearance for the melt stream to leak under pressure.

[0080] Although preferred embodiments of the present invention have been described, those of skill in the art will appreciate that variations and modifications may be made without departing from the spirit and scope thereof as defined by the appended claims. 

We claim:
 1. An injection molding apparatus comprising: a manifold having a manifold channel, said manifold channel having an inlet for receiving a melt stream of moldable material and an outlet for delivering said melt stream to a nozzle channel of a nozzle; a sealing element provided between said nozzle and said manifold, said sealing element including a melt channel for receiving said melt stream from said outlet of said manifold channel and delivering said melt stream to said nozzle channel; and a mold cavity for receiving said melt stream from said nozzle channel, said nozzle channel communicating with said mold cavity through a mold gate; wherein said sealing element has a higher thermal expansion coefficient than both said nozzle and said manifold.
 2. An injection molding apparatus as claimed in claim 1, wherein a recess is formed in a manifold contacting surface of said nozzle, said recess being sized to receive said sealing element.
 3. An injection molding apparatus as claimed in claim 2, wherein said melt channel of said sealing element provides a continuous path between said nozzle channel and said outlet of said manifold.
 4. An injection molding apparatus as claimed in claim 3, wherein in a cold condition, a clearance is provided between said sealing element and said manifold.
 5. An injection molding apparatus as claimed in claim 4, wherein said sealing element abuts said manifold at an operating temperature to provide a seal between said sealing element and said manifold.
 6. An injection molding apparatus as claimed in claim 5, wherein said sealing element is comprised of copper.
 7. An injection molding apparatus as claimed in claim 5, wherein said sealing element is comprised of beryllium copper.
 8. An injection molding apparatus as claimed in claim 5, wherein said sealing element is comprised of brass.
 9. An injection molding apparatus as claimed in claim 1, wherein a first recess is provided in an outlet surface of said manifold and a second recess is provided in a manifold contacting surface of said nozzle, said first recess and said second recess being aligned to receive said sealing element.
 10. An injection molding apparatus as claimed in claim 9, wherein in a cold condition, a clearance is provided between said sealing element and an offset surface of said first recess.
 11. An injection molding apparatus as claimed in claim 10, wherein at an operating temperature said sealing element abuts said offset surface of said first recess to provide a seal between said sealing element and said manifold.
 12. An injection molding apparatus as claimed in claim 11, wherein said sealing element is comprised of copper.
 13. An injection molding apparatus as claimed in claim 11, wherein said sealing element is comprised of beryllium copper.
 14. An injection molding apparatus as claimed in claim 11, wherein said sealing element is comprised of brass.
 15. An injection molding apparatus as claimed in claim 1, wherein said manifold includes a first recess provided in an outlet surface thereof for receiving said sealing element, said melt channel of said sealing element being aligned with said nozzle channel and said outlet of said manifold.
 16. An injection molding apparatus as claimed in claim 15, wherein in a cold condition a clearance is provided between a manifold contacting surface of said nozzle and said sealing element.
 17. An injection molding apparatus as claimed in claim 16, wherein in an operating condition a seal is provided between said sealing element and said manifold contacting surface of said nozzle.
 18. An injection molding apparatus as claimed in claim 17, wherein said sealing element is comprised of copper.
 19. An injection molding apparatus as claimed in claim 17, wherein said sealing element is comprised of beryllium copper.
 20. An injection molding apparatus as claimed in claim 17, wherein said sealing element is comprised of brass.
 21. An injection molding apparatus as claimed in claim 16, wherein said sealing element includes threads located on at least a portion of an outer surface thereof, said threads of said sealing element for mating with a threaded inner surface of said first recess
 22. An injection molding apparatus comprising: a manifold having a manifold channel for receiving a melt stream of moldable material under pressure; a manifold plug provided in said manifold, said manifold plug having a manifold plug channel formed therein, said manifold plug channel having an inlet for receiving said melt stream from said manifold channel and an outlet for delivering said melt stream to a nozzle channel of a nozzle; and a mold cavity for receiving said melt stream from said nozzle channel, said nozzle channel communicating with said mold cavity through a mold gate; wherein said manifold plug has a higher thermal expansion coefficient than both said nozzle and said manifold.
 23. An injection molding apparatus as claimed in claim 22, wherein in a cold condition, a clearance is provided between a lower edge of said manifold plug and a manifold contacting surface of said nozzle.
 24. An injection molding apparatus as claimed in claim 23, wherein in an operating condition said manifold plug abuts said manifold contacting surface of said nozzle to provide a seal between said manifold plug and said nozzle.
 25. An injection molding apparatus as claimed in claim 24, wherein said manifold plug is comprised of copper.
 26. An injection molding apparatus as claimed in claim 24, wherein said manifold plug is comprised of beryllium copper.
 27. An injection molding apparatus as claimed in claim 24, wherein said manifold plug is comprised of brass.
 28. An injection molding apparatus comprising: a manifold having a manifold channel, said manifold channel having an inlet for receiving a melt stream of moldable material under pressure and an outlet; a nozzle having nozzle body and a nozzle head, said nozzle head being located adjacent an outlet surface of said manifold, said nozzle having a nozzle channel for receiving said melt stream from said outlet of said manifold channel; and a mold cavity for receiving said melt stream from said nozzle channel, said nozzle channel communicating with said mold cavity through a mold gate; wherein at least a portion of said nozzle head has a higher thermal expansion coefficient than both said nozzle body and said manifold.
 29. An injection molding apparatus as claimed in claim 28, wherein in a cold condition a clearance is provided between said nozzle head and an outlet surface of said manifold.
 30. An injection molding apparatus as claimed in claim 29, wherein in an operating condition said nozzle head abuts said outlet surface of said manifold to provide a seal between said nozzle head and said manifold.
 31. An injection molding apparatus as claimed in claim 30, wherein said nozzle head is integral with said nozzle body. 